The latest development in synchronous wind turbine technology: how the LVS system can deliver low cost, broad-band variable turbine speed and type 5 grid connection

Synchronous wind turbines, directly gridconnected, provide about 10% of New Zealand's wind power at a 48 MW wind farm that has been running since 2006. A further 4 MW of these turbines have been installed in Scotland since 2013. In these turbines, the generator runs at constant speed (set by grid frequency) while the turbine rotor runs at variable speed (VS). This is achieved by having a differential stage in an otherwise conventional 3-stage gearbox, combined with a hydrostatic torque reaction system. Unlike other VS designs (hydraulic or electronic), this has the great virtue that the subsystem that it adds (hydraulic in this case) handles only 5% of the turbine power, and thus does not significantly increase the capital cost of the wind turbine. The net effect on wind turbine cost is neutral or a saving because the considerable cost of power electronic conversion (PEC, rated at up to 100% of turbine power) is eliminated.